Ultralong Cycle Stability and High Rate Performance of Aqueous Ammonium-Ion Hybrid Supercapacitors Enabled by In Situ Polymerization of PANI on Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub> MXene
Jing Pan, Weifeng Liu, Chengwei Zhan, Yuxuan Liu, Zhijin Zhao, Jinyu Sun, Haixia Li, Qingbo Liu, Lun Xiong
Abstract
Aqueous ammonium ion (NH 4 + ) hybrid supercapacitors (A-HSCs) have attracted considerable attention because of their safety, accessibility, and eco-friendliness. However, the development of suitable electrode materials, particularly for anodes, remains challenging. Although Ti 3 C 2 T x MXene exhibits considerable potential as an electrode material, its restacking tendency limits ion transport and electrochemical performance. In addition, previous studies mainly focused on acidic electrolytes, which can lead to poor stability and corrosion issues, highlighting the need to explore Ti 3 C 2 T x application in neutral NH 4 + -based electrolytes. In this study, we present a high-performance anode for A-HSCs constructed from Ti 3 C 2 T x /polyaniline composite materials. Compared with the original Ti 3 C 2 T x MXene, the enhanced interlayer spacing, improved conductivity, and enhanced stability of the composite resulted in a remarkable specific capacitance of 217 F g –1 at 1 A g –1 with 97% capacitance retention over 100,000 cycles at 20 A g –1 in a three-electrode system. Ex-situ XRD and XPS analyses confirmed the favorable and reversible NH 4 + storage behavior of the Ti 3 C 2 T x /PANI composite. The assembled A-HSCs demonstrated exceptional energy densities, exceeding 69.84 Wh kg –1 at a power density of 899.9 W kg –1 . Ti 3 C 2 T x /PANI-based microdevices fabricated using laser engraving technology retained 91.9% of the original capacitance at 10 A g –1 after 4000 cycles and maintained excellent performance under 180° bending. The findings of this study demonstrate Ti 3 C 2 T x /PANI’s potential for NH 4 + storage materials and offer insights into (NH 4 ) 2 SO 4 gel electrolytes for flexible A-HSCs.